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'78 280SEL RHD (UK) - heater problem #1

Started by joshm, 25 April 2010, 04:48 AM

joshm

Hi all,

Following on from a thread a hi-jacked earlier on (http://forum.w116.org/mechanicals/1973-280sel-(116-025)-heater-controls-water-entry) I wanted to ask for some help with a problem I rather stupidly created for myself.

My initial problem was that the heater blower wouldn't come on at all. I took out the motor and checked that still worked (which it did) and also cleaned up the connectors on the engine side of the bulkhead. This laster step resulted in some success, in the the motor started running as it wasa supposed to once (i.e. off when off, on low when at level 1 etc). However, on a second test it started blowing continuously, regardless of the dial setting.

At this point I thought I'd check out/clean up the connections at the back of the dial, so I took it out. Here's where my stupidity comes in - I took it out in too much of a hurry and didn't take note of the position/location of the 6 wires that were connected to 6 of the 8 pins on the back on the dial/controller.

I have tried various permutations and combinations in line with how I thought they looked like they went (based on the position of the wires and the kinks/bends) but this just resulted in a boat-load of blown fuses (fuse number 3 in my car, for what it's worth).

So what I'm wondering is anyone is able to tell me how to wire the controller up? I'll post a bunch of pictures below to show how I took it out and also to show the colours of the wires and the configuration of the controller pins.

Thanks for any assistance you can offer!

joshm

1 - popped off the dial to reveal the retaining nut




2 - removed the retaining nut (23mm?) and removed the fascia to reveal the black plastic mounting plate. the mounting plate is (was!) stapled onto the wood and comes away easily by pushing it back. To remove it you need to position it so that one ends pops out the aperture, and then the other.




3 - The controller (in my hand) and wires at the back can be seen. There may be a black plastic shroud covering the connections at the back (shown in this picture resting on the back of the controller)




4 - The wires, showing their colouring




5 - If you were wanting to remove the controller, you need to release the cable too. This is done by un-clipping the retaining strip as shown, and then turning the dial to III (max) and releasing the cable.







6 - the rear of the controller showing the pins


sannerud

#2
Lucky for you my mid-consol is not in the car at the moment...



(2:green 3:black-green stripe 4:green-white stripe 5:brown 6:green-yellow stripe) 8:green-red stripe

joshm

Awesome - thank you! I'll nip out and see if I can make your config work - I'll get back to you with my result.
;D

sannerud

#4
If your blower-motor is not working at all or blowing continuously the problem is most likely your pre-resistance which you will find in the other end of the cabels:




To get it out you must loosen the two screws over and under the cabels at the firewall (picture 1). Then follow the cabels from the blower-motor inside the dash and you will find the unit :)

joshm

Excellent! Thanks for this - we suspected that this was the unit at fault but were unsure of how to get at it. We used to have a spare unit in good condition, but unfortunately our cellar was flooded and it got drowned  :(

So I will attempt to get at this unit and clean it up. Once again, thank you for your help -  I may be back to ask for clarificition/assistance if I have trouble getting to it  ;D

sannerud

I had the same problem, suddenly the blower ran at full speed the moment i turn on the ignition, independent of the blowerswitch position. I replaced the pre-resistance unit and now it works fine. You need to take out the blower motor unit to get your hand up in the hole to get out the unit. Good luck :)

joshm

Quote from: sannerud on 25 April 2010, 06:16 AM
I had the same problem, suddenly the blower ran at full speed the moment i turn on the ignition, independent of the blowerswitch position. I replaced the pre-resistance unit and now it works fine. You need to take out the blower motor unit to get your hand up in the hole to get out the unit. Good luck :)

Do you think I'm wasting my time in trying to clean up the old unit? Should I wait until I can get a replacement rather than just try to fix the current one?

I took a quick look at where the wires from the blower motor went and they seem to disappear through a grommet into the large plastic enclosure used to channel the blown air. Does this sound right, and to get access to repair do you think I need to remove anything other than the blower motor?

Thanks! Josh

joshm

Well I tried to get access with the blower motor removed by reaching up into the gap with my arm, but I simply don't have enough joints or length in my arm to reach the unit. I'm sure I could remove the screws holding it on the bulkhead and pull the unit out, but my fear is that I would not be able to replace it if I can't physically touch it when in situ.

It looks like I may have to dismantle the whole assembly behind the glove box - any asvice or instructions for me?

Also, if you have a part number for the unit it'd be great if you could share it with me.

Thanks, Josh

Frankenstien

joshm ... I take it the dash center-mounted blower controller switch wiring puzzle got solved with sannerud's first photo-post ... and now you are focusing on re & re access to the pre-resistance unit ... sounds like progress is being made ... good luck in your efforts to get the old unit out, cleaned up and working again!  FFF

joshm

Quote from: Frankenstien on 25 April 2010, 10:07 AM
joshm ... I take it the dash center-mounted blower controller switch wiring puzzle got solved with sannerud's first photo-post ... and now you are focusing on re & re access to the pre-resistance unit ... sounds like progress is being made ... good luck in your efforts to get the old unit out, cleaned up and working again!  FFF

Yes, that's right. Likewise, I hope you're making progress with your own issues!

As an interim solution, I've done rather a nasty bodge and installed a toggle switch in the glove box so that I can kill the blower motor that way if & when it gets too irritating.
At some point (hopefully when I'm given some more tips on this thread!) I'll go back to the pre-resistance unit and address it properly.

Other jobs on the horizon - fixing the odometer and dash lighting, and sorting out the windshield, door & trunk seals  ::)

Cheers, Josh

sannerud

#11
The only number printed at the unit is 80086 and 26183. But I have a copy of the 1972 parts catalog. The number might not be right no more. But here at my local Mercedes shop in Norway they use the old partnumber and let the computer  transform it to a updated number if necessary. I hope this can help:





I did not try cleaning the unit (had a donor part) but my guess is that it will be waste of time... Maybe somebody else tried this...? When I replaced my unit my arm was just long enough to reach in (about 40cm into the hole) You need a helper under the hood to get the new one installed. (if your not a octopus) :)

joshm

Once again, thank you sannerud, you're a star. I'll get onto a dealer a know who should have a spare.

Frankenstien

joshm ... looks like I got the same problem now (full fan-speed heater/defroster blower motor) that you had back in April, 2010 ...

How did you ever make out with replacing the pre-resistance unit? (looks like #27, 'Series resistance', part # 116 835 00 06 in sannerud's « Reply #11 on: 25 April 2010, 01:33 PM »)

Or did cleaning up the old unit do the trick?

Probably a dumb question: you likely initially tried simply disconnecting / reconnecting the wiring plug from the pre-resistance unit from the engine side of the firewall to see if you could get the heater/defroster fan working properly again - right? ... or am I mis-understanding how it is mounted / connected?

Thanks, FFF

Frankenstien

 ... bump ... All ... I'm curious to know how the Heater / Defroster Blower motor Series Resistance module connector detaches from the engine side of the firewall ... I'd like to try DeoxIT D5 on the electrical contacts ... this would be the last ditch, fading hope of a guy being roasted out of the damn car with a constant full speed fan ... who doesn't want to have to try and reach the module (for replacement) from under the dash ... FFF